This is my own experience.
Earlier last year (2020), with the sudden 'work from home' that came into place, I had to rethink my network. Had a line with BT (FTTC). Speeds weren't that great, while price was very high, so thought I'd get an unlimited 3 sim.
A deal was on at that time, so price per month was great, albeit being on a 24 month contract. Tested a 3 sim - speed was decent/ok (approx 30-50 up 15-20 down), so went ahead and ordered the sim, purchased a basic Huawei router and was good to go. A couple of weeks later, started seeing speeds dropping. PING was extremely bad.
Researched and was suggestions it could be the router, so went for another 4G router, this time it cost over £150. That did show some increase in speed, but PING is still bad. We aren't even that far away from the 3 mast. Speed was slow for most of the day, and would speed up during the night, post 12am - till 6am.
It got to a point where it was unbearable, just two people using it, brought it to it's knees.
So, stuck on a 24 month contract, was left with no option but going back to a fixed line broadband, and opted with VM, the 350 package (due to the highest upload speed available in the area).
That has since worked wonders, ah, as well as multiple people working from home, home schooling, gaming, 4k on multiple TV's etc all working fine.
Long story short, I would advise strongly against it.
If you are able to, go for a fixed line, unless for some reason the sim card route is somehow more superior than the other options.
But I'm now left with two contracts (VM & Three 18 month and 24 month respectively). Three I can't even use as failover, as it crawls so slow.
Edited by JakeRoof (Mon 11-Jan-21 09:59:58)